Attachment of a decorative sheet (e.g., an adhesive-backed paint replacement film) or protective film (e.g., an adhesive-backed paint protection film) is known as a means for decorating and/or protecting an internal or external surface of a vehicle such as, e.g., an automobile, train, airplane, watercraft, or the like.
For example, Japanese Unexamined Patent Application Publication No. 2010-260942 describes a multilayer film capable of attachment by accommodating numerous surface shapes, that has good curved surface followability, and that has excellent durability after attachment, where the multilayer film includes a surface protection layer formed from a surface protection film and a metal thin film layer. Based on a thermoplastic straight-chain molecular weight structure in the polyurethane of the surface protection layer, a branched structure is appropriately arranged by branching by crosslinking. Thus, due to the use of cyclohexane in the backbone of the molecule, high moldability and weather resistance are both realized. In order to handle as a coatable liquid the polyurethane having a molecular weight of at least several tens of thousands, the polyurethane is used as an aqueous dispersion, i.e. an aqueous polyurethane dispersion (PUD).
A decorative sheet (e.g., an adhesive-backed paint replacement film) used for vehicle applications, such as for an automobile, train, airplane, watercraft, or the like, is required to have decorative performance (i.e. multiple colors, patterns, textures, or the like) and simultaneously to have water resistance and alcohol resistance, particularly when used for exterior decoration. That is to say, when the decorative sheet has been exposed to rain for a long time period, peeling, swelling, discoloration, or the like failures must not occur when alcohol-containing window washer, water repellant, or other chemicals become attached to the decorative sheet. However, since water dispersed polyurethanes generally have good hydrophilicity, the polyurethane is readily permeated by water and alcohol. As a result, water resistance and alcohol resistance of the polyurethane are low. When a surfactant is jointly used in a top layer for exterior use in order to blend in a photostabilizer, UV absorbent, or the like for weather resistance of the top layer itself or for protection of a lower layer, hydrophilicity increases further, and resistance becomes inferior. Thus, the film is required to have even greater water resistance and alcohol resistance.